I. Field of the Invention
The present invention relates to communications. More particularly, the present invention relates to a system and method for base station initiated call setup.
II. Description of the Related Art
The use of code division multiple access (CDMA) techniques is one of several techniques for facilitating communications in which a large number of system users are present. Although other techniques such as time division multiple access (TDMA), frequency division multiple access (FDMA), and amplitude modulation (AM) schemes such as amplitude companded single sideband (ACSSB) are known, CDMA has significant advantages over these other techniques. The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Pat. No. 4,901,307, entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS," assigned to the assignee of the present invention and incorporated by reference herein.
In the wireless CDMA system, a large number of wireless subscriber units, each having a transceiver, communicates through satellite repeaters or terrestrial stations which are also referred to as cells. Each cell includes a physical plant called a base station. A cell covers a limited geographic area and routes calls carried over subscriber units to and from a telecommunication network via a mobile switching center. When a subscriber moves into the geographic area of a new cell, the routing of that subscriber's call may be eventually made through the new cell by a process called a "handoff."
A subscriber unit transmits a signal that is received by a base station. The signal is then relayed to a mobile switching center which in turn routes the signal to the public switched telephone network and to telephone lines or other subscriber units. Similarly, a signal may be transmitted from the public switched telephone network to a subscriber unit via a base station and a mobile switching center. The communications channel allocated for communication of information between the subscriber unit and the base station is called the traffic channel.
The interface between the subscriber unit and the base station is referred to as the air interface. The telecommunications industry association (TIA) has provided a standard for CDMA call processing on the air interface entitled "IS-95-A Mobile Station--Base Station Compatibility Standard for Dual Mode Wideband Spread Spectrum Cellular System," which is incorporated by reference herein. The interface between the base station and the mobile switching center is referred to as the A interface. The TIA has provided for call processing on the A interface through the standard provided in "IS-634 Mobile Switching Center--Base Station Interface for Public 800 MHz," which is also incorporated herein by reference. IS-95-A and IS-634 both define the messages and signals that are sent on their respective interfaces for the operation of a CDMA wireless system.
The call flow in a CDMA system requires processing on both the air interface and the A interface. The successful progression of a call requires that the proper messages and signals are sent at the right times on both the air interface and the A interface. The IS-634 standard is being developed to provide for call processing on the A interface. A number of problems and deficiencies are present in IS-634 which currently does not support some of the necessary operations on the A interface.
One deficiency in IS-634 is in the lack of support for base station initiated call setup. Although IS-634 provides procedures for supporting subscriber unit initiated and network initiated call setup, procedures are needed to enable the base station to initiate call setup. Base station initiated call setup is needed for several reasons, such as the support of base station originated test calls and the support of packet data services calls.
Test calls are important during the initial deployment and reengineering of the base station. The purpose of these calls is to generate statistics and analysis data which are specific to the base station. The data includes the frame error rate and link capacity estimates. These measurements are used as guidelines for properly configuring the base station.
Two types of test calls are the loopback call and the Markov call. The loopback call provides a loopback of traffic frames through a subscriber unit. It provides a means for a base station to supply a sequence of data blocks (frames) to a subscriber unit so that the transmitting and receiving performance can be measured. Using the loopback service option, the base station generates and sends traffic frames to the subscriber unit. After a delay to allow for processing, the mobile station sends the received frames back to the base station. The base station may then compare the transmitted frame with the received frame to determine if there was a frame error during the two-way transmission. The Markov call provides pseudo-random data for testing the traffic channel. The data is generated to emulate the characteristics of a voice/data call without having to involve actual users. Thus, pseudo-random data generated at a base station is transmitted to a subscriber unit, which performs frame error rate calculations and generates other statistics to characterize the quality of the link. Base station initiated call setup is necessary for the base station to initiate the loopback and Markov test calls.
Base station initiated call setup is also needed to support packet data services calls. In some situations, packet data services call may arrive for a subscriber unit either from a packet data network connected to a base station or a packet data network connected to a mobile switching center. When a packet data services call arrives via a base station, the base station must be able to initiate call setup in order to deliver the call to the subscriber unit.
In other situations, base station initiated call setup may be used to reactivate a packet data services call which is in a dormant mode. After a packet call has been set up, the call may enter a dormant mode if no packets are being transmitted for a period of time. In the dormant mode, the traffic channel is released. If packets are again received from the internet, the call needs to be reactivated, and the traffic channel needs to be set up again. Base station initiated call setup may be used to reactivate the dormant call.
These deficiencies are recognized and solved by the present invention in the manner described below.